feat(models): 组织、用户、角色、客户、会话与消息模型

按组织边界定义数据关系，补齐仓储层与通用工具，迁移脚本可重复执行。

backend/app/models/faq.py

@@ -0,0 +1,119 @@
+"""
+Copyright 2024-2026 ReplyPier
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+"""
+
+import enum
+import uuid
+
+from sqlalchemy import Column, DateTime, ForeignKey, Index, Integer, String, Text
+from sqlalchemy.dialects.postgresql import UUID
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+
+from app.database import Base
+
+DEFAULT_FAQ_CATEGORY = "General"
+# Column widths, kept here so the API schemas bound input to exactly what the
+# columns accept instead of restating the numbers (see models.schemas.faq).
+FAQ_SLUG_MAX_LENGTH = 80
+FAQ_META_TITLE_MAX_LENGTH = 120
+FAQ_META_DESCRIPTION_MAX_LENGTH = 300
+FAQ_URL_PATH_MAX_LENGTH = 400
+FAQ_SOURCE_URL_MAX_LENGTH = 2048
+
+
+class FAQStatus(str, enum.Enum):
+    DRAFT = "draft"
+    PUBLISHED = "published"
+
+
+class FAQ(Base):
+    """A single question/answer pair shown on the org's public help center.
+
+    FAQs are a standalone projection of the knowledge base: generation only
+    reads knowledge content, and editing/deleting FAQs never touches the
+    knowledge tables. Drafts stay private until explicitly published.
+    """
+    __tablename__ = "faqs"
+
+    id = Column(UUID(as_uuid=True), primary_key=True, default=uuid.uuid4)
+    # No single-column index: both composite indexes below lead with org id.
+    organization_id = Column(
+        UUID(as_uuid=True),
+        ForeignKey("organizations.id", ondelete="CASCADE"),
+        nullable=False,
+    )
+    question = Column(Text, nullable=False)
+    # Answer is authored/stored as Markdown; rendered to sanitized HTML on the
+    # public article page (app.services.help_center_content).
+    answer = Column(Text, nullable=False)
+    # URL slug for the public article page (/a/{slug}). Assigned from the
+    # question at creation and kept stable so published article URLs don't churn
+    # on edits — but editable by hand for SEO (app.api.help_center.faqs).
+    # Unique per org (see ix_faqs_org_slug); NULL until assigned.
+    slug = Column(String(FAQ_SLUG_MAX_LENGTH), nullable=True)
+    # The original URL path of an article migrated in from another help center.
+    # When set, the article is SERVED at this exact path and /a/{slug} 301s to
+    # it, so the org keeps the URLs it already ranks for instead of losing that
+    # SEO to a migration. Root-relative, no trailing slash, and percent-DECODED
+    # because that is the form the ASGI scope hands us to match against (every
+    # emitted URL re-encodes it — see help_center_seo.article_url).
+    # Unique per org (see ix_faqs_org_url_path); NULL means "served at /a/{slug}",
+    # which is every article that wasn't migrated.
+    url_path = Column(String(FAQ_URL_PATH_MAX_LENGTH), nullable=True)
+    # Where an imported article was fetched from, post-redirect. Provenance only
+    # — never routed on — and kept even when url_path had to be dropped, so the
+    # original URL is still recoverable.
+    source_url = Column(String(FAQ_SOURCE_URL_MAX_LENGTH), nullable=True)
+    # Per-article SEO overrides for the public page's <title> and meta
+    # description. NULL means "derive from the content": the question and an
+    # excerpt of the answer (see app.api.help_center_public). Lengths mirror
+    # help_center_settings.title/description.
+    meta_title = Column(String(FAQ_META_TITLE_MAX_LENGTH), nullable=True)
+    meta_description = Column(String(FAQ_META_DESCRIPTION_MAX_LENGTH), nullable=True)
+    # Free-form category assigned by the LLM grouping step (or the user).
+    category = Column(String(100), nullable=False, default=DEFAULT_FAQ_CATEGORY)
+    # Plain string (values from FAQStatus), like knowledge_queue.status — new
+    # states never need an ALTER TYPE migration.
+    status = Column(String, nullable=False, default=FAQStatus.DRAFT)
+    # Provenance: the knowledge source it was generated from (if any) plus a
+    # human-readable label ("example.com/docs", "Imported from support.x.com",
+    # "Added manually") that survives source deletion.
+    knowledge_id = Column(Integer, ForeignKey("knowledge.id", ondelete="SET NULL"), nullable=True, index=True)
+    source_label = Column(String(255), nullable=True)
+    generation_job_id = Column(
+        Integer, ForeignKey("faq_generation_jobs.id", ondelete="SET NULL"), nullable=True, index=True
+    )
+    created_by = Column(UUID(as_uuid=True), ForeignKey("users.id", ondelete="SET NULL"), nullable=True)
+    sort_order = Column(Integer, nullable=False, default=0)
+    # "Was this helpful?" tallies (de-duplicated per IP/day at the API).
+    helpful_yes = Column(Integer, nullable=False, default=0, server_default="0")
+    helpful_no = Column(Integer, nullable=False, default=0, server_default="0")
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    updated_at = Column(DateTime(timezone=True), onupdate=func.now())
+
+    organization = relationship("Organization")
+    knowledge = relationship("Knowledge")
+
+    __table_args__ = (
+        Index("ix_faqs_org_status", "organization_id", "status"),
+        Index("ix_faqs_org_category", "organization_id", "category"),
+        # Serves the public /a/{slug} lookup and enforces per-org uniqueness.
+        # Multiple NULL slugs coexist (Postgres treats NULLs as distinct).
+        Index("ix_faqs_org_slug", "organization_id", "slug", unique=True),
+        # Serves the preserved-path lookup made for any URL no other public
+        # route claimed, and enforces per-org uniqueness. NULLs coexist.
+        Index("ix_faqs_org_url_path", "organization_id", "url_path", unique=True),
+    )